We get our ivermectin pour-on at our local TSC (Tractor Supply Company). You can also find it a Jeffers Livestock (online).
It's called Iver-On Pour On for cattle. You don't need to inject it. It's a simple topical treatment that you rub in behind the ear.
Here is the link for the weight chart and instructions for use:
Iver-On Pour On.
If you're not willing to take him to the vet for treatment, please get the pour-on and start treating immediately. Normal treatment is every 7-10 days for 3-weeks. It could take up to 5 treatments for relief in the case of a stubborn flare-up.
It sounds like you need to get your pig to a good cavy saavy vet. He has gone too long without attention and treatment. His symptoms are pretty severe.